What is the difference between java.lang.Void and void?

Question

In API

\"The Void class is an uninstantiable placeholder class to hold a reference to the Class object representing the Java keyword void.\"

Answer 1

Void is useful because sometimes you need to specify the return type of a method outside the method itself.

For example take this java 8 lambda expression, which checks whether an EventResource object has certain properties, using a method called checkBenefitConcertInCentralPark, passed into the method checkCreatedEvent:

eventChecker.checkCreatedEvent(TestEvents::checkBenefitConcertInCentralPark);

The checkBenefitConcertInCentralPark method is defined like this (note the use of Void):

    public static Void checkBenefitConcertInCentralPark(EventResource eventResource) { 
        // JUnit code here...
        // assertThat(blablabla  :)  )

        return null; // we can only return null at the end of a method when returning Void
    }

and then the checkBenefitConcertInCentralPark method is passed into the method checkCreatedEvent.

    // Function describes the checkBenefitConcertInCentralPark method
    public void checkCreatedEvent(Function function) { 
        function.apply(this.eventResource);
    }